The present invention refers to an improved apparatus for handling, on a large-scale basis and in an orderly sequential manner, preforms made of thermoplastic material, in particular polyethylene terephtalate (PET) and polypropylene (PP), adapted to be blow-moulded for conversion into finished containers.
In particular, the present invention can be used in a most advantageous manner when the described apparatus is associated with an integrated type of production plant (i.e. a plant that is also known in the art as a single-stage plant), but can of course also be effectively used in connection with plants that are fed with previously produced preforms to only carry out the final blow-moulding phase (two-stage plants).
As a matter of fact, these processes for the production of such types of containers are generally known to be able to be schematically divided into two basic topologies, i.e., single-stage and two-stage processes.
In two-stage processes, a previously moulded preform or parison in a substantially amorphous state is heated up again to its preferred molecular orientation temperature, at which it is then blow-moulded to the desired shape. As used in this particular context, the term xe2x80x9ctwo-stage processxe2x80x9d, or simply xe2x80x9ctwo-stagexe2x80x9d, is intended to mean any process that produces a preform or panson which must subsequently be heated up again from ambient temperature to the respective blow-moulding temperature.
On the contrary, single-stage processes are so defined due to the fact that they are capable of moulding the so-called preform or parison, and transferring the same preform or parison from the injection or extrusion mould (after it has cooled down to some appropriate temperature) to a conditioning station where the preform or parison is allowed to evenly cool down to a preferred molecular orientation temperature. The preform or parison a then transferred to a blow-moulding mould, where it is moulded into the desired shape.
Both above types of production methods involve the use of a (per se known) blow-moulding station and the therewith associated handling means for transferring and releasing the preforms and/or the blow-moulded containers after the blow-moulding phase. Both types of processes further share the feature of transferring the injection moulded or extruded preforms first to a conditioning and temperature-levelling station and then from this station to the actual blow moulding plant.
Such a transferring operation is usually carried out with the use of various techniques and according to various methods. In particular, this is carried out by contemporaneously transferring groups of preforms to the conditioning station and then, again in a synchronous manner, transferring them to the blow moulding unit where the group of preforms is processed simultaneously.
A different technique makes, on the contrary, use of the concept calling for a plurality of preforms to be first transferred in an orderly but sequential manner to the conditioning station, where they are treated by allowing them to move in a continuous manner through conditioning ovens or zones. After such a conditioning phase, the preforms are picked on a one-by-one basis and transferred into appropriate blow-moulding tools where they are eventually converted into finished containers with a similar process that is, however, appropriately set to follow an out-of-phase pattern from mould to mould according to the rate of arrival of the preforms. This second technique has some advantages from both a construction and an operational point of view, as anyone skilled in the art is well aware of, so that they shall not be reviewed here.
It, however, also has a typical drawback connected with the fact that the conditioning phase is particularly facilitated by the vertical position of the preform. However, with the neck portion thereof turned downwards for largely known reasons, mounting the preform on the means provided to transfer it first to the conditioning station and then to the blow moulding unit is on the contrary carried out with the preform that although in a vertical position, has its neck portion turned upwards. As a result, if use is made of a transferring means operating on a single plane, be it a vertical or horizontal one, a serious drawback is incurred in the conditioning phase the preforms undergo conditioning with their neck portion turned upwards. Alternatively, remarkable complications in the construction and, therefore, also the operation of the plant shall be created, with a clearly heavy impact on the overall economics thereof if preforms are transferred with their neck portion turned downwards.
Eloquent disclosures of such a technique making use of transferring means moving on a single plane are described in the following patent literature: U.S. Pat. No. 3,984,513, U.S. Pat. No. 4,362,498, WO 89/01400, WO 95/05933. U.S. Pat. No. 3,339,230, U.S. Pat. No. 4,354,813, U.S. Pat. No. 4,313,720. U.S. Pat. No. 4,850,850, EP 0 296 825, EP 0 425 360.
A general temperature conditioning plant for preforms is known from the patent publication FR 2 646 632 to SIDEL, which is used with devices that are capable of reversing the orientation of the preforms twice. Therefore, the same preforms end up eventually acquiring their initial orientation.
With such devices, the preforms which reach the temperature conditioning plant with their neck portion facing upwards are turned upside down, so that their neck portion is facing downwards. In such a position they are then subjected to temperature conditioning. After such a treatment they are again turned 180xc2x0 so as to regain their initial position (i.e., with position with their neck portion facing upwards), which is more favorable in view of the subsequent handling thereof.
However, such devices, which comprise a helical guiding system and roller-type following members, turn out to be rather complicated and, therefore, expensive and inherently unreliable. This is because each preform must be provided with a single device capable of quickly reversing its position on an individual basis.
Based on the above considerations, it is therefore a main purpose of the present invention to provide an apparatus and a method of preform transferring and conditioning phases preceding the actual blow-moulding phase, in which the orientation of the preforms will be adjusted in the most effective, economical and reliable manner, while doing away with the above drawbacks. In addition, the invention is further capable of feeding the blow moulding plant in a continuous, automatic and orderly manner without any interposition of phases that may interrupt the continuity of the preform feeding flow. Furthermore, such an apparatus must be easily implemented with the use of readily available techniques and means and shall therefore be reasonably low in its overall costs.
Such main aim of the present invention, along with further features thereof, is reached in an apparatus that is made and operates as recited in the appended claims.